1. Field of the Invention
The invention relates to a plug-type clasp for pieces of jewelry, in particular necklaces. The invention is particularly directed to a clasp having a housing, the front end of which is acted on internally by one end of a spring. The other end of the spring acts on a sleeve which is movable inside the housing and which has a receiving opening directed towards the other end of the housing. A connecting part can be inserted into this receiving opening via an opening in one end of the housing, and locked there.
2. Prior Art
A plug-type clasp having a structure of this type is disclosed in EP No. 0 121 953-A1, particular reference being made to FIG. 3 of that publication. In this known plug-type clasp, the sleeve movably placed in the housing has at least two flexible tongues or clamps pointing in the direction of the insertion opening, which are guided by a constriction of the housing in the form of an envelope of a cone in such a way that the clamps engage, via protrusions, an annular groove of the connecting part. This engagement position is secured by the action of the spring. When opening this known plug-type clasp it is necessary to grip the housing, to draw back the sleeve against the force of the spring, and to remove the connecting part from the receiving opening of the sleeve. Because at this position the sleeve is in direct connection with the other connecting end of the plug-type clasp, it may happen that an unintended pull at that connecting end of the sleeve will displace the sleeve in the housing against the force of the spring so that its front engaging tongue will release the annular groove of the connecting part. As a result, when a pull is exerted on both sides of the plug-type clasp, it is possible that unintended opening of the clasp, and thus a possible loss of the piece of jewelry, may occur. Manufacture of the sleeve with both the formed connecting end and the flexible tongues is relatively costly.
Because the connecting end disclosed in the above-cited publication is of the eyelet type, it is apparent that this connecting end is intended for connection to corresponding eyelets or components of the connected piece of jewelry, for example a necklace, which are also capable of transferring axial forces such as are required in this case for opening the clasp, i.e., by an axial pull which displaces the sleeve against the housing.
However, there are also other possibilities for attaching and connecting a necklace, for example, to such a clasp. Such attachment may be effected, for example, by techniques such as crimping or riveting. However, connections of this type are not highly resistant to axial stress so that they can be broken relatively easily if pulled. For this reason the known plug-type clasp is not suitable for such uses.